One of techniques to improve a fuel economy of a vehicle includes an idle stop control technique which automatically stops an engine when a predetermined condition such that a stopped state with no intention to start the vehicle is elapsed by a set time during a vehicle stopped state is established.
This idle stop control technique also serves to restart the engine automatically in response to a release of the idle stop, when such an operation of a vehicle driver that a brake pedal is released so that a brake is transferred from an operation state to a non-operation state is preformed in order for the vehicle driver intentionally to make the start of the vehicle.
On the other hand, a transmission is gear shift controlled according to a hydraulic pressure from an engine driven oil pump driven by the engine.
Incidentally, since, during the idle stop, the engine is not driven, the hydraulic pressure from the engine driven oil pump is not present, and a starting frictional element of the transmission is in a release state, the transmission is in a power transmission disabled state.
When, in these states, the engine is restarted in response to the release of the idle stop, the hydraulic pressure from the engine driven oil pump driven by the engine is generated so that the transmission is in a power transmission enabled state.
However, a response delay occurs from a time of the generation of the hydraulic pressure due to the restart of the engine to a time of the power transmission enabled state according to an engagement of the starting frictional element.
When an idle stop release time control which makes the engine a state responding to the driving operation is performed during the above-described response delay, a rising engine output according to this idle stop release time control is inputted to the transmission (in the power transmission disabled state) before the power transmission enabled state, such a problem occurs that an ill influence is given on a durability of the transmission.
A technique has, heretofore, been proposed in which the starting frictional element of the transmission is stroke operated into a state immediately before the start of the engagement (a state immediately before an engagement capacity is started to have in the starting frictional element) according to a working oil from the electrically-powered oil pump in place of the engine driven oil pump during the idle stop and, thus, the transmission is held in the state immediately before the power transmission start, as described, for example, in a patent document 1.
According to this technique, during the idle stop, in order to hold the transmission in the state immediately before the power transmission start by stroking operation the starting frictional element into the state immediately before the engagement start according to the working oil from the electrically-driven oil pump, the working oil from the engine driven oil pump can speedily be started to engage the starting frictional element when the engine is restarted in response to the release of the idle stop. Thus, at the time of restart of the engine, the transmission can speedily fall into the power transmission enabled state. Hence, a rising engine torque according to the restart is not inputted to the transmission (in the state in which the power transmission is disabled) before the power transmission enabled state so that the problem such that the ill influence is given on the durability of the transmission can be eliminated.
Pre-Published Document
Patent Document
Patent document 1: Japanese Patent Application First Publication (tokkai) No. 2001-041067 official Gazette (FIG. 3 column 6)